Treatment of friedel-crafts reaction liquors



Patented June 17, 1941 OFFICE 'rmiarmr or FRIEDEL-CBAFTS aasc'rloiv LIQUons mm A. Robinson, Midland, Mlch., assignor to The Dow Chemical Company, Midland, Mich., a corporation Michigan No Drawing. Application February 15, 1939, Serial No. 56,599

6 chum. (01. 260-671 The present invention relates to a process for the removal of dispersed organo-metal halide complex catalysts oi the Priedel-Oraits type from reaction liquors obtained in the alkylation of aromatic compounds.

As is well known, the active catalyst in a model-Crafts reaction is not the metal halide originally added, but is an organo-metal halide complex compound which is usually present as a brown sludge-like mass suspended in the reaction liquor. In thepreparation of alkylated aromatic compounds according to the Friedel- Crai'ts synthesis, the usual Procedure is to introducean olefin or alkyl halide into an agitated mixture of an aromatic hydrocarbon or halohydrocarbon and an organo-metal halide complex catalyst. Then, when the desired amount of alkylating agent has been added, agitation of the reaction mixture is discontinued. The major portion of the suspended catalyst settles to the bottom of the reaction vessel and may be withdrawn for reuse in subsequent alkylations. However, an appreciable quantity of the cranemetal halide complex catalyst never settles from the reaction liquor, butreinains dissolved or otherwise dispersed in the crude reaction prodnot, and cannot be. removed by physical means. The presence of this dispersed catalyst in the crude alkylated product greatly complicates the separation and purification of the alkylated compounds formed in the reaction, particularly in large scale or continuous operation. Thus when attempt is made to separate the individual products by fractional distillation without first removing the dispersed organo-metal halide, this material tends to catalyze decomposition and rearrangement of the alkylated products during the distillation process, and hence to reduce the yields of the desired compolmds. Further, the dispersed catalyst itself tends to decompose on the heating surfaces or the distilling apparatus. forming tars and scaly deposits which decrease the rate of heat transfer through the still body and necessitate fre uent cleaning operations.

To avoid these diiilculties. it is customary to wash the crude alkylated product with an excess of cold water or aqueous alkali in order chemically to destroy the dispersed organo-metal halide complex prior to the distillation step. Unfortunately, this procedure is disadvantageous in that the addition or water or aqueous solutions wets the crude product and necessitates the introduction of a drying operation before distillation. It the drying is not conducted with extreme care, equivalent corrosion problems are encountered inthe subsequent steps or the process. -Moreover, the treatment with water frequently entails iurther difllculties resulting from emulsifloat-ion oi the aqueous phase in the crude allzylated product. All these drawbacks have seriously limited the application of the Friedel- Crafts reaction to industrial chemical syntheses.

The chief object oi the present invention is to provide a method of removing the dispersed organo-metal halide complex catalyst from Friedel- Crafts alkylation liquors which eliminates the distillation dimculties hereinbeiore mentioned, and at the same time avoids the disadvantages oi catalystrmoval with water or aqueous solutions.

According to the invention, a dispersed organo-metal halide catalyst may be effectively removed from a Friedel-Crafts alkylation liquor by treating the liquor with a small proportion oi an organic nitrogenous base. The dispersed organc-metal complex is thereby converted to a flocculent precipitate which has no catalytic properties and does not interfere with subsequent distillation or other treatment of the alkylation liquor. v

In an alkylation process utilizing the invention, an olei'in or alkyl halide is first reacted with an aromatic hydrocarbon or halohydrocarbon according to the usual Friedel-Craits reaction procedures, in either a batchwise or continuous proc- V ess. The resulting reaction liquor is usually allowed to stand for some time to permit settling and removal of the bulk of the sludge-like organo-metal halide catalyst, although this step is not essential. Then, according to the invention, the crude reaction product containing the remaining dispersed organo-metal halide complex catalyst is mixed with a small proportion of an organic nitrogenous base. Such reagents react rapidly with the dispersed catalyst complex to form a flocculent precipitate which setties to the bottom of the reaction vessel and may be removed, if desired, by'flltration or otherwise. The crude alkylation liquor thus treated may be iractionally distilled in the customary manner to separate the alkylated productswithout danger of catalytic deoompositionf The flocculent precipitate i'ormed in'the process resembles a metal hydroxide in its physical characteristics. The chemical identity of the material has not been clearly established.

The exact proportion of organicnitrogenous base to be added in the process cannot be stated in advance since it depends upon the particular alkylation being carried out, the precise nature of the catalystemployedthe concentration of catslyst, and the reaction conditions. In practice, the organic base is added in small portions until further addition does not result in theiormation of additional precipitate. A slight excess of the reagent is not disadvantageous. In general,

an amount is required corresponding to between about 0.2 and about 12.0 gram-moles oi nitrogenous base .per gram-atom or metal present in the catalyst to be removed. When the dispersed catalyst complex is present in ordinary concentration, i. e., after the bulk of the catalyst has been allowed .to settle out, this Proportion of nitrogenous base is equivalent to between about 0.005 and about 1.0 part by weight 01' organic base per 100 parts of liquor to be treated. In practice, it is not usually necessary to adjust the temperature 01 the crude alkylated product before the nitrogenous base is added since the process is operable at any temperature between about C. and about 150 C. In many instances, however, e. g., in the preparation of ethylbcnzene, temperatures 01' C. to 75 C. are preterable. i

In practice, the nitrogenous base may be added as such to the crude reaction liquor or it may be dissolved in any suitable non-aqueous solvent miscible with the reaction liquor, preferably in an aromatic hydrocarbon such as benzene. In so far as I am aware,any organic nitrogenous base containing a trivalent nitrogen atom may be employed. Thus I may use an aliphatic primary, secondary, or tertiary amine, such as anhydrous methyl amine, diethyl amine, tri-isobutyl amine, etc., an aliphatic amino-alcohol such as ethanol amine, tri-ethanol amine, di-amino is'opropanol, and the like, an aromatic or hydroaromatic amine such as aniline, dimethyl aniline, parabrom aniline, cyclohexyl amine, or a heterocyclic nitrogen base such as morpholine, pyridine, or quinoline. However, for many reactions, especially on a laboratory scale, the use of high-boil ing nitrogenous bases, such as quinoline. is oite advantageous.

The present process is particularly adapted to the removal of dispersed complex catalysts from alkylation liquors formed in the reaction of lower oleflns or lower alkyl monohalides, such as ethylene, propylene, isobutylene, ethyl chloride, isopropyl bromide, mixtures of these substances,

etc., with aromatic hydrocarbons or halohydro-' carbons, such as benzene, ethylbenzene, chlorobenzene, isopropyl brombenzene, naphthalene, etc. The treatment is applicable to the removal not only of aluminum chloride complexes, but

also of organo-metal halide complex catalysts formed from other meta-1 halides of the Friedel- Crafts type, c. g. aluminum bromide, ferric chloride, stannic chloride, antimony trichloride, etc.

It will be appreciated from the foregoing that the invention provides a simple process for removing dispersed organo-metal halide complex stated by any of the following claims or the equivalent of such stated step or steps be em-.

ployed.

I claim: 1. In a process for the preparation oi alkylated aromatic compounds wherein an alkylating agent' selected from the class consisting of lower oleflnes and lower alkyl monohalides is reactedwithacompound selected from the class consisting of arcmatic hydrocarbons and halohydrocarbons in the presence of an organo-metal halide complex catalyst or the Friedel-Crafts type to form a crude alkylated product, the step of removing dispersed organo-metal halide complex catalyst from the crude alkylated product which comprises treating said crude product with a small proportion of an organicnitrogenous base under substantially anhydrous conditions.

2. In a process for the preparation oi alkylated aromatic compounds wherein an alkylating agent selected from the class consisting of lower olelines and lower alkyl monohalides is reacted with a compound selected from the class consisting of aromatic hydrocarbons and halohydrocarbons in the presence of an organo-metal halide complex catalyst oithe Friedel-Crafts type to form a crude alkylated product, and wherein the major portion of the catalyst is then separated trom the crude product, the step of removing any remaining dispersed organo-metal halide complex catalyst from the crude alkylated product which comprises treating said product with a small proportion of an organic nitrogenous base under sub- 'stantially anhydrous conditions.

3. In a process for the preparation 01! ethyl benzene wherein ethylene is reacted with benzene in the presence of an aluminum chloride complex cataylst of the Friedel-Crafts type to form a crude ethyl benzene, and wherein the major portion of the catalyst is then separated from the crude ethyl benzene, the step of removing any remaining dispersed complex catalyst from the crude ethyl benzene which comprises treating the crude ethyl benzene at a temperature between about 10 catalysts from Friedel-Crafts alkylatlon liquors At the same and about C. with an organic nitrogenous base in the proportion of between about 0.005 and about 1.0 part of base per parts otcrude ethyl benzene under substantially anhydrous conditions.

4. In a process for the preparation of alblated aromatic compounds wherein an alkylating agent selected from the class consisting of lower oleiines and lower alkyl monohalides is reacted with a compound selected from the class consisting of aromatic hydrocarbons and halohydrocarbons in the presence of an organo-metal halide complex catalyst oi the Friedel-Craits type to form a crude alkylat'ed product, thestep of removing dispersed organo-metal halide complex catalyst from the crude alkylated product which comprises treating said crude product with a small propor-- tion of an organic nitrogenous base selected from- HAROLD A. ROBINSON. 

